The structure of the twenty-nine residue peptide hormone glucagon is to be studied by physical and chemical techniques for the purpose of relating its structure to its biological function. Chemical modifications include methylation of Met-27 and subsequent demethylation, addition of CO2 to the alpha-amino group of His-1, removal of Asn-28 and Thr-29 by carboxypeptidase A treatment of the sulfonium derivative followed by demethylation and finally removal of His-1. This latter is to be followed by addition of an extra residue to His-1 and replacement of His-1. Physical and chemical studies include circular dichroism, 13C NMR, binding assays and amino acid analyses. Biological assays include activation of adenyl cyclase of crude rat liver plasma membranes and the effects upon lipogenesis in hepatocyte cell culture systems. The results should be valuable for understanding the role and mechanism of action of specific portions of the molecule in physiological and pathological states.